Claim for Priority
[0001] This application is based upon United States Patent Application Serial No.
12/221,141, filed July 31, 2008, of the same title, the priority of which is hereby claimed and the disclosure of
which is incorporated herein by reference.
Field of the Invention
[0002] The present invention relates generally to a process for the production of ethanol
from acetic acid. More specifically, the present invention relates to a process including
hydrogenating acetic acid utilizing a catalyst composed of platinum and tin supported
on a suitable catalyst support optionally containing one or more additional hydrogenating
metals to form ethanol with high selectivity.
Background
[0003] There is a long felt need for an economically viable process to convert acetic acid
to ethanol. Ethanol is an important commodity feedstock for a variety of industrial
products and is also used as a fuel additive with gasoline. For instance, ethanol
can readily be dehydrated to ethylene, which can then be converted to polymer products
or small-molecule based products for use in coatings, polymer manufacture and so forth.
Ethanol is conventionally produced from feedstocks where price fluctuations are becoming
more significant. That is, fluctuating natural gas and crude oil prices contribute
to fluctuations in the cost of conventionally produced, petroleum, natural gas or
corn or other agricultural product-sourced ethanol, making the need for alternative
sources of ethanol all the greater when oil prices and/or agricultural product prices
rise.
[0004] It has been reported that ethanol can be produced from the hydrogenation of acetic
acid, but most of these processes feature several drawbacks for a commercial operation.
For instance, United States Patent No.
2,607,807 discloses that ethanol can be formed from acetic acid over a ruthenium catalyst at
extremely high pressures of 700-950 bars in order to achieve yields of around 88%,
whereas low yields of only about 40% are obtained at pressures of about 200 bar. Nevertheless,
both of these conditions are unacceptable and uneconomical for a commercial operation.
[0005] More recently, it has been reported that ethanol can be produced from hydrogenating
acetic acid using a cobalt catalyst again at superatmospheric pressures such as about
40 to 120 bar.
See, for example, United States Patent No.
4,517,391 to Shuster et al. However, the only example disclosed therein employs reaction pressure in the range
of about 300 bar still making this process undesirable for a commercial operation.
In addition, the process calls for a catalyst containing no less than 50 percent cobalt
by weight plus one or more members selected from the group consisting of copper, manganese,
molybdenum, chromium, and phosphoric acid, thus rendering the process economically
non-viable. Although there is a disclosure of use of simple inert catalyst carriers
to support the catalyst materials, there is no specific example of supported metal
catalysts.
[0006] United States Patent No.
5,149,680 to Kitson et al. describes a process for the catalytic hydrogenation of carboxylic acids and their
anhydrides to alcohols and/or esters utilizing a platinum group metal alloy catalysts.
The catalyst is comprised of an alloy of at least one noble metal of Group VIII of
the Periodic Table and at least one metal capable of alloying with the Group VIII
noble metal, admixed with a component comprising at least one of the metals rhenium,
tungsten or molybdenum. Although it has been claimed therein that improved selectivity
to alcohols are achieved over the prior art references it was still reported that
3 to 9 percent of alkanes, such as methane and ethane are formed as by-products during
the hydrogenation of acetic acid to ethanol under their optimal catalyst conditions.
[0007] United States Patent No.
4,777,303 to Kitson et al. describes a process for the productions of alcohols by the hydrogenation of carboxylic
acids. The catalyst used in this case is a heterogeneous catalyst comprising a first
component which is either molybdenum or tungsten and a second component which is a
noble metal of Group VIII of the Periodic Table of the elements, optionally on a support,
for example, a high surface area graphitized carbon. The selectivity to a combined
mixture of alcohol and ester is reported to be only in the range of about 73 to 87
percent with low conversion of carboxylic acids at about 16 to 58 percent. In addition,
no specific example of conversion of acetic acid to ethanol is provided.
[0008] United States Patent No.
4,804,791 to Kitson et al. describes another process for the production of alcohols by the hydrogenation of
carboxylic acids. In this process, ethanol is produced from acetic acid or propanol
is produced from propionic acid by contacting either acetic acid or propionic acid
in the vapor phase with hydrogen at elevated temperature and a pressure in the range
from 1 to 150 bar in the presence of a catalyst comprising as essential components
(i) a noble metal of Group VIII of the Periodic Table of the elements, and (ii) rhenium,
optionally on a support, for example a high surface area graphitized carbon. The conversion
of acetic acid to ethanol ranged from 0.6 % to 69% with selectivity to ethanol was
in the range of about 6% to 97%.
[0009] From the foregoing it is apparent that existing processes do not have the requisite
selectivity to ethanol or existing art employs catalysts, which are expensive and/or
non-selective for the formation of ethanol and produces undesirable by-products.
Summary of the Invention
[0010] Surprisingly, it has now been unexpectedly found that ethanol can be made on an industrial
scale directly from acetic acid with very high selectivity and yield. More particularly,
this invention provides a process for the selective formation of ethanol from acetic
acid comprising: hydrogenating acetic acid over a platinum/tin hydrogenating catalyst
in the presence of hydrogen. More specifically, the catalyst suitable for the process
of this invention is comprised of a combination of platinum and tin supported on a
suitable catalyst support optionally in combination with one or more metal catalysts
selected from the group consisting of palladium, rhodium, ruthenium, rhenium, iridium,
chromium, copper, molybdenum, tungsten, vanadium and zinc. Suitable catalyst supports
include without any limitation, silica, alumina, calcium silicate, carbon, zirconia
and titania.
Detailed Description of the Invention
[0011] The invention is described in detail below with reference to numerous embodiments
for purposes of exemplification and illustration only. Modifications to particular
embodiments within the spirit and scope of the present invention, set forth in the
appended claims, will be readily apparent to those of skill in the art.
[0012] Unless more specifically defined below, terminology as used herein is given its ordinary
meaning. Mole percent (mole % or %) and like terms refer to mole percent unless otherwise
indicated. Weight percent (wt % or %) and like terms refer to weight percent unless
otherwise indicated.
[0013] "Conversion" is expressed as a mole percentage based on acetic acid in the feed.
The conversion of acetic acid (AcOH) is calculated from gas chromatography (GC) data
using the following equation:

[0014] "Selectivity" is expressed as a mole percent based on converted acetic acid. For
example, if the conversion is 50 mole % and 50 mole % of the converted acetic acid
is converted to ethanol, we refer to the ethanol selectivity as 50%. Selectivity is
calculated from gas chromatography (GC) data using the following equation:

[0015] Weight percent of a catalyst metal is based on metal weight and the total dry weight
of metal and support.
[0016] The reaction proceeds in accordance with the following chemical equation:

[0017] In accordance with the invention, conversion of acetic acid to ethanol can be carried
out in a variety of configurations, such as for example in a single reaction zone
which may be a layered fixed bed, if so desired. An adiabatic reactor could be used,
or a shell and tube reactor provided with a heat transfer medium could be used. The
fixed bed can comprise a mixture of different catalyst particles or catalyst particles
which include multiple catalysts as further described herein. The fixed bed may also
include a layer of particulate material making up a mixing zone for the reactants.
A reaction mixture including acetic acid, hydrogen and optionally an inert carrier
gas is fed to the bed as a stream under pressure to the mixing zone. The stream is
subsequently supplied (by way of pressure drop) to the reaction zone or layer. Reaction
zone comprises a catalytic composition including a suitable hydrogenating catalyst
where acetic acid is hydrogenated to produce ethanol. Any suitable particle size may
be used depending upon the type of reactor, throughput requirements and so forth.
[0018] Although various platinum containing hydrogenating catalysts known to one skilled
in the art can be employed in hydrogenating acetic acid to form ethanol in the process
of this invention it is preferred that a hydrogenating catalyst employed contains
a combination of platinum and tin on a suitable catalyst support. As noted earlier,
it is further preferred that the catalysts that are suitable in the process of this
invention contain optionally a third metal supported on the same catalyst support.
The following metals may be mentioned as those metals suitable as a third metal without
any limitation: palladium, rhodium, ruthenium, rhenium, iridium, chromium, copper,
molybdenum, tungsten, vanadium, zinc and a mixture thereof. Typically, it is preferred
that a suitable weight ratio of a combination of platinum and tin on a suitable support
can be used as a hydrogenating catalyst. Thus a combination of platinum and tin (Pt/Sn)
in the weight ratio of about 0.1-2 are particularly preferred. More preferably, a
weight ratio of Pt/Sn is about 0.5 -1.5 and most preferably the weight ratio of Pt/Sn
is about 1. Preferred examples of metals that can be used with Pt/Sn as a third metal
include without any limitation any of the other metals listed above, such as for example
rhodium, iridium, copper, molybdenum and zinc.
[0019] Various catalyst supports known in the art can be used to support the catalysts of
this invention. Examples of such supports include without any limitation, zeolite,
iron oxide, silica, alumina, titania, zirconia, magnesium oxide, calcium silicate,
carbon, graphite and a mixture thereof. Preferred supports are silica, alumina, calcium
silicate, carbon, zirconia and titania. More preferably silica is used as a catalyst
support in the process of this invention. It is also important to note that higher
the purity of silica better it is preferred as a support in this invention. Another
preferred catalyst support is calcium silicate.
[0020] In another embodiment of this invention the preferred catalyst support is carbon.
Various forms of carbon known in the art that are suitable as catalyst support can
be used in the process of this invention. Particularly preferred carbon support is
a graphitized carbon, particularly the high surface area graphitized carbon as described
in Great Britain Patent No.
2,136,704. The carbon is preferably in particulate form, for example, as pellets. The size
of the carbon particles will depend on the pressure drop acceptable in any given reactor
(which gives a minimum pellet size) and reactant diffusion constraint within the pellet
(which gives a maximum pellet size).
[0021] The carbon catalyst supports that are suitable in the process of this invention are
preferably porous carbon catalyst supports. With the preferred particle sizes the
carbon will need to be porous to meet the preferred surface area characteristics.
[0022] The catalyst supports including the carbon catalyst supports may be characterized
by their BET, basal plane, and edge surface areas. The BET surface area is the surface
area determined by nitrogen adsorption using the method of
Brunauer Emmett and Teller J. Am. Chem. Soc. 60,309 (1938). The basal plane surface area is the surface area determined from the heat of adsorption
on the carbon of n-dotriacontane from n-heptane by the method described in
Proc. Roy. Soc. A314 pages 473-498, with particular reference to page 489. The edge surface area is the surface area
determined from the heat of adsorption on the carbon of n-butanol from n-heptane as
disclosed in the
Proc. Roy. Soc. article mentioned above with particular reference to page 495.
[0023] The preferred carbon catalyst supports for use in the present invention have a BET
surface area of at least 100 m
2/g, more preferably at least 200 m
2/ g, most preferably at least 300 m
2 /g. The BET surface area is preferably not greater than 1000 m
2/g, more preferably not greater than 750 m
2/g.
[0024] It is preferred to use carbon catalyst supports with ratios of basal plane surface
area to edge surface area of at least 10:1, preferably at least 100:1. It is not believed
that there is an upper limit on the ratio, although in practice it will not usually
exceed 200:1.
[0025] The preferred carbon support may be prepared by heat treating a carbon-containing
starting material. The starting material may be an oleophillic graphite e.g. prepared
as disclosed in Great Britain Patent No.
1,168,785 or may be a carbon black.
[0026] However, oleophillic graphites contain carbon in the form of very fine particles
in flake form and are therefore not very suitable materials for use as catalyst supports.
We prefer to avoid their use. Similar considerations apply to carbon blacks which
also have a very fine particle size.
[0027] The preferred materials are activated carbons derived from vegetable materials e.g.
coconut charcoal, or from peat or coal or from carbonizable polymers. The materials
subjected to the heat treatment preferably have particle sizes not less than these
indicated above as being preferred for the carbon support.
[0028] The preferred starting materials have the following characteristics: BET surface
area of at least 100, more preferably at least 500 m
2/g.
[0029] The preferred heat treatment procedure for preparing carbon supports having the defined
characteristics, comprise successively (1) heating the carbon in an inert atmosphere
at a temperature of from 900°C to 3300°C, (2) oxidizing the carbon at a temperature
between 300°C and 1200°C, (3) heating in an inert atmosphere at a temperature of between
900°C and 3000°C.
[0030] The oxidation step is preferably carried out at temperatures between 300° and 600°C
when oxygen (e.g. as air) is used as the oxidizing agent.
[0031] The duration of the heating in inert gas is not critical. The time needed to heat
the carbon to the required maximum temperature is sufficient to produce the required
changes in the carbon.
[0032] The oxidation step must clearly not be carried out under conditions such that the
carbon combusts completely. It is preferably carried out using a gaseous oxidizing
agent fed at a controlled rate to avoid over oxidation. Examples of gaseous oxidizing
agents are steam, carbon dioxide, and gases containing molecular oxygen e.g. air.
The oxidation is preferably carried out to give a carbon weight loss of at least 10
weight percent based on weight of carbon subjected to the oxidation step, more preferably
at least 15 weight percent.
[0033] The weight loss is preferably not greater than 40 weight percent of the carbon subjected
to the oxidation step, more preferably not greater than 25 weight percent of the carbon.
[0034] The rate of supply of oxidizing agent is preferably such that the desired weight
loss takes place over at least 2 hours, more preferably at least 4 hours.
[0035] Where an inert atmosphere is required it may be supplied by nitrogen or an inert
gas.
[0036] As noted above, the loading levels of platinum and tin are generally referenced with
the content of platinum and the weight ratio of Pt/Sn and is in the range of about
0.1 to 2. Thus, when the weight ratio of Pt/Sn is 0.1, the amount of platinum can
be 0.1 or 1 weight percent and thus 1 or 10 weight percent of tin is present on the
catalyst support. More preferably, the weight ratio of Pt/Sn is about 0.5, and thus
the amount of platinum on the catalyst support can be either 0.5 or 1 weight percent
and that of tin is either one or two weight percent. More preferably, the weight ratio
of Pt/Sn is one. Thus the amount of platinum on a support is 0.5, one or two weight
percent and that of tin is also 0.5, one or two weight percent. However, low weight
ratios of Pt/Sn can also be employed. For instance, a weight ratio of Pt/Sn of 0.2
can also be employed. In such cases, the amount of platinum on the support can be
0.5 or one weight percent whereas 2.5 or five weight percent of tin is employed.
[0037] The amount of third metal loading if present on a support is not very critical in
this invention and can vary in the range of about 0.1 weight percent to about 10 weight
percent. A metal loading of about 1 weight percent to about 6 weight percent based
on the weight of the support is particularly preferred.
[0038] The metal impregnation can be carried out using any of the known methods in the art.
Typically, before impregnation the supports are dried at 120°C and shaped to particles
having size distribution in the range of about 0.2 to 0.4 mm. Optionally the supports
may be pressed, crushed and sieved to a desired size distribution. Any of the known
methods to shape the support materials into desired size distribution can be employed.
[0039] For supports having low surface area, such as for example alpha-alumina, the metal
solutions are added in excess until complete wetness or excess liquid impregnation
so as to obtain desirable metal loadings.
[0040] As noted above, the hydrogenation catalysts used in the process of this invention
are at least bimetallic containing platinum and tin. Generally, without intending
to be bound by any theory, it is believed that one metal acts as a promoter metal
and the other metal is the main metal. For instance, in the instant process of the
invention, combination of platinum and tin is considered to be main metal for preparing
hydrogenation catalysts of this invention. However, it can also be considered that
platinum is the main metal and tin is the promoter metal depending upon various reaction
parameters including but not limited to catalyst support employed, reaction temperature
and pressure, etc. The main metal can be combined with a promoter metal such as tungsten,
vanadium, molybdenum, chromium or zinc. However, it should be noted that sometimes
main metal can also act as a promoter metal or vice versa. For example, nickel can
be used as a promoter metal when iron is used as a main metal. Similarly, chromium
can be used as a main metal in conjunction with copper (i.e., Cu-Cr as main bimetallic
metals), which can further be combined with promoter metals such as cerium, magnesium
or zinc.
[0041] The bimetallic catalysts are generally impregnated in two steps. First, the "promoter"
metal is added, followed by "main" metal. Each impregnation step is followed by drying
and calcination. The bimetallic catalysts may also be prepared by co-impregnation.
For instance, the platinum/tin catalysts of this invention are generally co-impregnated
on a support catalyst. In the case of trimetallic Cu/Cr-containing catalysts as described
above, a sequential impregnation may be used, starting with the addition of the "promoter"
metal. The second impregnation step may involve co-impregnation of the two principal
metals, i.e., Cu and Cr. For example, Cu-Cr-Co on SiO
2 may be prepared by a first impregnation of chromium nitrate, followed by the co-impregnation
of copper and cobalt nitrates. Again, each impregnation is followed by drying and
calcinations. In most cases, the impregnation may be carried out using metal nitrate
solutions. However, various other soluble salts which upon calcination releases metal
ions can also be used. Examples of other suitable metal salts for impregnation include
metal oxalate, metal hydroxide, metal oxide, metal acetate, ammonium metal oxide,
such as ammonium heptamolybdate hexahydrate, metal acids, such as perrhenic acid solution,
and the like.
[0042] Thus in one embodiment of this invention, there is provided a hydrogenation catalyst
wherein the catalyst support is graphite with a bimetallic loading of platinum and
tin. In this aspect of the invention, the loading of platinum is about 0.5 weight
percent to about 1 weight percent and the loading of tin is about 0.5 weight percent
to about 5 weight percent. Specifically, platinum/tin loading levels of 1/1, 1/5,
0.5/0.5, and 0.5/2.5 weight percent on graphite can be used.
[0043] In another embodiment of this invention, there is further provided a hydrogenation
catalyst wherein the catalyst support is high purity low surface area silica with
a bimetallic loading of platinum and tin. In this aspect of the invention, the loading
platinum is about 0.5 weight percent to about 1 weight percent and the loading of
tin is about 0.5 weight percent to about 5 weight percent. Specifically, platinum/tin
loading levels of 1/1, 1/5, 0.5/0.5, and 0.5/2.5 weight percent on high purity low
surface area silica can be used.
[0044] In another embodiment of this invention, there is further provided a hydrogenation
catalyst wherein the catalyst support is calcium silicate with a bimetallic loading
of platinum and tin. In this aspect of the invention, the loading platinum is about
0.5 weight percent to about 1 weight percent and the loading of tin is about 0.5 weight
percent to about 5 weight percent. Specifically, platinum/tin loading levels of 1/1,
1/5, 0.5/0.5, and 0.5/2.5 weight percent on calcium silicate can be used.
[0045] In another embodiment of this invention, there is further provided a hydrogenation
catalyst wherein the catalyst support is a silica-alumina with a bimetallic loading
of platinum and tin. In this aspect of the invention, the loading platinum is about
0.5 weight percent to about 1 weight percent and the loading of tin is about 0.5 weight
percent to about 5 weight percent. Specifically, platinum/tin loading levels of 1/1,
1/5, 0.5/0.5, and 0.5/2.5 weight percent on calcium silicate can be used.
[0046] In general, by the practice of this invention acetic acid can selectivity be converted
to ethanol at very high rates. The selectivity to ethanol in general is very high
and may be at least 60 percent. Under preferred reaction conditions, acetic acid is
selectively converted to ethanol at a selectivity of at least 80 percent or more preferably
at a selectivity of at least 90 percent. Most preferably ethanol selectivity is at
least 95 percent.
[0047] The conversion of acetic acid using the catalysts of this invention is at least 60%
with selectivity to ethanol at least 80%, preferably 90% and most preferably 95%.
[0048] Generally, the active catalysts of the invention are the non-promoted catalysts containing
platinum and tin supported on silica with platinum and tin loadings of 1 weight percent
each. In accordance with the practice of this invention, acetic acid can be converted
using these catalysts at conversions of around 90% with ethanol selectivity of at
least 90%, more preferably selectivity to ethanol of at least 95%.
[0049] Similar conversions and selectivities are achieved using calcium silicate, graphite
or silica-alumina as a support and with loadings of platinum and tin of one weight
percent each and with no other promoter metals.
[0050] In another aspect of this invention it is also possible to obtain high levels of
conversions in the order of at least 90% and high selectivity to ethanol of at least
about 90% using platinum and tin loadings of one weight percent each on silica or
calcium silicate as catalyst supports with a promoter metal, such as for example cobalt,
ruthenium or palladium. The promoter metal loadings is in the range of about 0.1 weight
percent to about 0.5 weight percent, more preferably in the range of about 0.15 weight
percent to 0.3 weight percent and most preferably the promoter metal loading is about
0.2 weight percent. In this aspect of the invention, other preferred catalyst supports
include silica-alumina, titania or zirconia.
[0051] In another aspect of the process of this invention, the hydrogenation is carried
out at a pressure just sufficient to overcome the pressure drop across the catalytic
bed.
[0052] The reaction may be carried out in the vapor or liquid state under a wide variety
of conditions. Preferably, the reaction is carried out in the vapor phase. Reaction
temperatures may be employed, for example in the range of about 200°C to about 300°C,
preferably about 225°C to about 275°C. The pressure is generally uncritical to the
reaction and subatmospheric, atmospheric or superatmospheric pressures may be employed.
In most cases, however, the pressure of the reaction will be in the range of about
1 to 30 atmospheres absolute, most preferably the pressure of reaction zone is in
the range of about 10 to 25 atmospheres absolute.
[0053] Although the reaction consumes two moles of hydrogen per mole of acetic acid to produce
a mole of ethanol, the actual molar ratio of acetic acid to hydrogen in the feed stream
may be varied between wide limits, e.g. from about 100:1 to 1:100. It is preferred
however that such ratio be in the range of about 1:20 to 1:2. More preferably the
molar ratio of acetic acid to hydrogen is about 1:5.
[0054] The raw materials used in connection with the process of this invention may be derived
from any suitable source including natural gas, petroleum, coal, biomass and so forth.
It is well known to produce acetic acid through methanol carbonylation, acetaldehyde
oxidation, ethylene oxidation, oxidative fermentation, and anaerobic fermentation
and so forth. As petroleum and natural gas have become more expensive, methods for
producing acetic acid and intermediates such as methanol and carbon monoxide from
alternate carbon sources have drawn more interest. Of particular interest is the production
of acetic acid from synthesis gas (syngas) that may be derived from any suitable carbon
source. United States Patent No.
6,232,352 to Vidalin, the disclosure of which is incorporated herein by reference, for example, teaches
a method of retrofitting a methanol plant for the manufacture of acetic acid. By retrofitting
a methanol plant the large capital costs associated with CO generation for a new acetic
acid plant are significantly reduced or largely eliminated. All or part of the syngas
is diverted from the methanol synthesis loop and supplied to a separator unit to recover
CO and hydrogen, which are then used to produce acetic acid. In addition to acetic
acid, the process can also be used to make hydrogen which is utilized in connection
with this invention.
[0055] United States Patent No.
RE 35,377 Steinberg et al., also incorporated herein by reference, provides a method for the production of methanol
by conversion of carbonaceous materials such as oil, coal, natural gas and biomass
materials. The process includes hydrogasification of solid and/or liquid carbonaceous
materials to obtain a process gas which is steam pyrolized with additional natural
gas to form synthesis gas. The syngas is converted to methanol which may be carbonylated
to acetic acid. The method likewise produces hydrogen which may be used in connection
with this invention as noted above.
See also, United States Patent No.
5,821,111 Grady et al., which discloses a process for converting waste biomass through gasification into
synthesis gas as well as United States Patent No.
6,685,754 Kindig et al., the disclosures of which are incorporated herein by reference.
[0056] The acetic acid may be vaporized at the reaction temperature, and then it can be
fed along with hydrogen in undiluted state or diluted with a relatively inert carrier
gas, such as nitrogen, argon, helium, carbon dioxide and the like.
[0057] Alternatively, acetic acid in vapor form may be taken directly as crude product from
the flash vessel of a methanol carbonylation unit of the class described in United
States Patent No.
6,657,078 of Scates et al., the disclosure of which is incorporated herein by reference. The crude vapor product
may be fed directly to the reaction zones of the present invention without the need
for condensing the acetic acid and light ends or removing water, saving overall processing
costs.
[0058] Contact or residence time can also vary widely, depending upon such variables as
amount of acetic acid, catalyst, reactor, temperature and pressure. Typical contact
times range from a fraction of a second to more than several hours when a catalyst
system other than a fixed bed is used, with preferred contact times, at least for
vapor phase reactions, between about 0.5 and 100 seconds.
[0059] Typically, the catalyst is employed in a fixed bed reactor e.g. in the shape of an
elongated pipe or tube where the reactants, typically in the vapor form, are passed
over or through the catalyst. Other reactors, such as fluid or ebullient bed reactors,
can be employed, if desired. In some instances, it is advantageous to use the hydrogenation
catalysts in conjunction with an inert material to regulate the pressure drop, flow,
heat balance or other process parameters in the catalyst bed including the contact
time of the reactant compounds with the catalyst particles.
[0060] In one of the preferred embodiments there is also provided a process for selective
and direct formation of ethanol from acetic acid comprising: contacting a feed stream
containing acetic acid and hydrogen at an elevated temperature with a suitable hydrogenating
catalyst containing about 0.5 weight percent to about 1 weight percent of platinum
and about 0.5 weight percent to about 5 weight percent of tin on a suitable catalyst
support and optionally a third metal supported on said support and wherein said third
metal is selected from the group consisting of cobalt, ruthenium and palladium.
[0061] In this embodiment of the process of this invention, the preferred hydrogenation
catalyst contains about one (1) weight percent platinum and about one (1) weight percent
tin. In this embodiment of the process of this invention it is preferred that the
hydrogenation catalysts is layered in a fixed bed and the reaction is carried out
in the vapor phase using a feed stream of acetic acid and hydrogen in the molar range
of about 1:20 to 1:5 and at a temperature in the range of about 225°C to 275°C and
at a pressure of reaction zones in the range of about 10 to 25 atmospheres absolute,
and the contact time of reactants is in the range of about 0.5 and 100 seconds.
[0062] The following examples describe the procedures used for the preparation of various
catalysts employed in the process of this invention.
Example A
Preparation of 1 weight percent platinum and 1 weight percent tin on Graphite
[0063] Powdered and meshed graphite (100 g) of uniform particle size distribution of about
0.2 mm was dried at 120°C in an oven under nitrogen atmosphere overnight and then
cooled to room temperature. To this was added a solution of platinum nitrate (Chempur)
(1.64 g) in distilled water (16 ml) and a solution of tin oxalate (Alfa Aesar) (1.74
g) in dilute nitric acid (1N, 8.5 ml). The resulting slurry was dried in an oven gradually
heated to 110°C (>2 hours, 10°C/min.). The impregnated catalyst mixture was then calcined
at 400°C (6 hours, 1°C/min).
Examples B
Preparation of 0.5 weight percent platinum and 5 weight percent tin on High Purity
Low Surface Area Silica
[0064] Powdered and meshed high purity low surface area silica (100 g) of uniform particle
size distribution of about 0.2 mm was dried at 120°C in an oven under nitrogen atmosphere
overnight and then cooled to room temperature. To this was added a solution of platinum
nitrate (Chempur) (0.82 g) in distilled water (8 ml) and a solution of tin oxalate
(Alfa Aesar) (8.7 g) in dilute nitric acid (1N, 43.5 ml). The resulting slurry was
dried in an oven gradually heated to 110°C (>2 hours, 10°C/min.). The impregnated
catalyst mixture was then calcined at 500°C (6 hours, 1°C/min).
Example C
Preparation of 1 weight percent platinum and 1 weight percent tin on High Purity Low
Surface Area Silica
[0065] The procedures of Example B was substantially repeated except for utilizing a solution
of platinum nitrate (Chempur) (1.64 g) in distilled water (16 ml) and a solution of
tin oxalate (Alfa Aesar) (1.74 g) in dilute nitric acid (1N, 8.5 ml).
Example D
Preparation of 1 weight percent platinum and 1 weight percent tin on Calcium Silicate
[0066] The procedures of Example B was substantially repeated except for utilizing a solution
of platinum nitrate (Chempur) (1.64 g) in distilled water (16 ml) and a solution of
tin oxalate (Alfa Aesar) (1.74 g) in dilute nitric acid (1N, 8.5 ml), and utilizing
calcium silicate as a catalyst support.
Example E
Preparation of 0.5 weight percent platinum, 0.5 weight percent tin and 0.2 weight
percent cobalt on High Purity Low Surface Area Silica
[0067] Powdered and meshed high purity low surface area silica (100 g) of uniform particle
size distribution of about 0.2 mm was dried at 120°C in an oven under nitrogen atmosphere
overnight and then cooled to room temperature. To this was added a solution of platinum
nitrate (Chempur) (0.82 g) in distilled water (8 ml) and a solution of tin oxalate
(Alfa Aesar) (0.87 g) in dilute nitric acid (1N, 4.5 ml). The resulting slurry was
dried in an oven gradually heated to 110°C (>2 hours, 10°C/min.). The impregnated
catalyst mixture was then calcined at 500°C (6 hours, 1°C/min). To this calcined and
cooled material was added a solution of cobalt nitrate hexahydrate (0.99 g) in distilled
water (2 ml). The resulting slurry was dried in an oven gradually heated to 110°C
(>2 hours, 10°C/min.). The impregnated catalyst mixture was then calcined at 500°C
(6 hours, 1°C/min).
Example F
Preparation of 0.5 weight percent tin on High Purity Low Surface Area Silica
[0068] Powdered and meshed high purity low surface area silica (100 g) of uniform particle
size distribution of about 0.2 mm was dried at 120°C in an oven under nitrogen atmosphere
overnight and then cooled to room temperature. To this was added a solution of tin
oxalate (Alfa Aesar) (1.74 g) in dilute nitric acid (1N, 8.5 ml). The resulting slurry
was dried in an oven gradually heated to 110°C (>2 hours, 10°C/min.). The impregnated
catalyst mixture was then calcined at 500°C (6 hours, 1°C/min).
Gas Chromatographic (GC) analysis of the Products
[0069] The analysis of the products was carried out by online GC. A three channel compact
GC equipped with one flame ionization detector (FID) and 2 thermal conducting detectors
(TCDs) was used to analyze the reactants and products. The front channel was equipped
with an FID and a CP-Sil 5 (20 m) + WaxFFap (5 m) column and was used to quantify:
Acetaldehyde
Ethanol
Acetone
Methyl acetate
Vinyl acetate
Ethyl acetate
Acetic acid
Ethylene glycol diacetate
Ethylene glycol
Ethylidene diacetate
Paraldehyde
[0070] The middle channel was equipped with a TCD and Porabond Q column and was used to
quantify:
CO2
Ethylene
Ethane
[0071] The back channel was equipped with a TCD and Molsieve 5A column and was used to quantify:
Helium
Hydrogen
Nitrogen
Methane
Carbon monoxide
[0072] Prior to reactions, the retention time of the different components was determined
by spiking with individual compounds and the GCs were calibrated either with a calibration
gas of known composition or with liquid solutions of known compositions. This allowed
the determination of the response factors for the various components.
Example 1
[0073] The catalyst utilized was 1 weight percent platinum and 1 weight percent tin on silica
prepared in accordance with the procedure of Example C.
[0074] In a tubular reactor made of stainless steel, having an internal diameter of 30 mm
and capable of being raised to a controlled temperature, there are arranged 50 ml
of 1 weight percent platinum and 1 weight percent tin on silica. The length of the
catalyst bed after charging was approximately about 70 mm.
[0075] A feed liquid was comprised essentially of acetic acid. The reaction feed liquid
was evaporated and charged to the reactor along with hydrogen and helium as a carrier
gas with an average combined gas hourly space velocity (GHSV) of about 2500 hr
-1 at a temperature of about 250°C and pressure of 22 bar. The resulting feed stream
contained a mole percent of acetic acid from about 4.4% to about 13.8% and the mole
percent of hydrogen from about 14% to about 77%. A portion of the vapor effluent was
passed through a gas chromatograph for analysis of the contents of the effluents.
The selectivity to ethanol was 93.4% at a conversion of acetic acid of 85%.
Example 2
[0076] The catalyst utilized was 1 weight percent platinum and 1 weight percent tin on calcium
silicate prepared in accordance with the procedure of Example D.
[0077] The procedure as set forth in Example 1 is substantially repeated with an average
combined gas hourly space velocity (GHSV) of 2,500 hr
-1 of the feed stream of the vaporized acetic acid and hydrogen at a temperature of
250°C and pressure of 22 bar. A portion of the vapor effluent is passed through a
gas chromatograph for analysis of the contents of the effluents. The acetic acid conversion
is greater than 70% and ethanol selectivity is 99%.
Comparative Example
[0078] The catalyst utilized was 1 weight percent tin on low surface area high purity silica
prepared in accordance with the procedure of Example F.
[0079] The procedure as set forth in Example 1 is substantially repeated with an average
combined gas hourly space velocity (GHSV) of 2,500 hr
-1 of the feed stream of the vaporized acetic acid and hydrogen at a temperature of
250°C and pressure of 22 bar. A portion of the vapor effluent is passed through a
gas chromatograph for analysis of the contents of the effluents. The acetic acid conversion
is less than 10% and ethanol selectivity is less than 1%.
[0080] While the invention has been illustrated in connection with particular examples,
modifications to these examples within the spirit and scope of the invention will
be readily apparent to those of skill in the art. In view of the foregoing discussion,
relevant knowledge in the art and references discussed above in connection with the
Background and Detailed Description, the disclosures of which are all incorporated
herein by reference, further description is deemed unnecessary.
1. A process for selective and direct formation of ethanol from a carbon source comprising:
(a) converting the carbon source into acetic acid; and
(b) contacting a feed stream containing the acetic acid and hydrogen in vapor form
at a temperature of 200ºC to 300ºC with a hydrogenating catalyst containing a combination
of platinum and tin on a catalyst support.
2. The process according to claim 1, wherein the catalyst support is selected from the
group consisting of silica, alumina, silica-alumina, calcium silicate, carbon, zirconia,
titania, and combinations thereof.
3. The process according to claim 1, wherein at least about 80% by weight of the acetic
acid consumed is converted to ethanol.
4. The process according to claim 1, wherein the carbon source is selected from the group
consisting of natural gas, petroleum, and coal.
5. The process according to claim 1, wherein the carbon source is biomass.
6. The process according to claim 5, wherein the converting of the biomass to the acetic
acid comprises the steps of:
(i) converting said biomass into a first stream comprising syngas;
(ii) catalytically converting at least some of said syngas into a second stream comprising
methanol;
(iii) separating some of said syngas into hydrogen and carbon monoxide; and
(iv) catalytically converting at least some of said methanol with some of said carbon
monoxide into a third stream comprising the acetic acid, and wherein the contacting
comprises reducing at least some of the acetic acid with some of said hydrogen into
a fourth stream comprising the ethanol.
7. The process according to claim 1, further comprising converting the carbon source
into methanol and converting the methanol into the acetic acid wherein the contacting
comprises reducing at least some of the acetic acid into the ethanol.
8. The process according to claim 1, further comprising converting the carbon source
into syngas, converting at least some of the syngas into methanol, and converting
the methanol into the acetic acid, wherein the contacting comprises reducing at least
some of the acetic acid stream into the ethanol.
9. The process according to claim 1, further comprising converting the carbon source
into syngas, separating a portion of the syngas into a hydrogen stream and carbon
monoxide stream, reacting a portion of the carbon monoxide stream with methanol into
the acetic acid, wherein the contacting comprises reducing at least some of the acetic
acid with some of said hydrogen stream into the ethanol.
10. The process according to claim 1, further comprising converting the carbon source
into syngas, separating a portion of the syngas into a hydrogen stream and carbon
monoxide stream, converting at least some of the syngas into methanol, reacting a
portion of the carbon monoxide stream with a portion of the methanol into the acetic
acid, wherein the contacting comprises reducing at least some of the acetic acid with
some of said hydrogen stream into the ethanol.
11. The process according to Claim 1, wherein the reactants consist of acetic acid and
hydrogen with a molar ratio in the range of 100:1 to 1:100, and the pressure of reaction
zones is in the range of 1 to 30 atmospheres absolute.
12. The process according to Claim 1, wherein the catalysts support contains a combination
of platinum and tin at a Pt/Sn weight ratio in the range of 0.1 to 2.
13. The process according to Claim 1, wherein the hydrogenation catalyst further contains
a third metal selected from the group consisting of palladium, rhodium, rhenium, iridium,
chromium, copper, molybdenum, tungsten, vanadium and zinc.
14. The process according to Claim 1, wherein the hydrogenation catalyst further contains
a third metal selected from the group consisting of rhodium, iridium, copper, molybdenum
and zinc.
15. The process according to Claim 1, wherein the hydrogenation catalyst further contains
a third metal selected from the group consisting of palladium, and cobalt.